This invention relates to a method and apparatus for measuring blood glucose concentration using glucose which is present at the buccal mucosal surface, and more particularly to an apparatus and method for measuring blood glucose concentration by means of the peroxidative enzyme glucose oxidase.
In general, an enzymatic electrode is often used to measure the level of a blood substance. A typical enzymatic electrode combines enzymatic and polarographic technologies. The enzyme is usually bound, physically or chemically, to an inert support.
Many enzymatic electrodes utilize enzymes which catalyze the peroxidative oxidation of a substrate and generate hydrogen peroxide. The specificity of the electrode is determined by the substrate specificity of the enzyme. Two types of analytical measurements are possible, each one using the polarographic technique. Specifically, either the consumption of free oxygen or the production of hydrogen peroxide may be measured. Both serve as stoichiometric indicators of substrate oxidation. When the enzyme electrode is used after it has been calibrated using known concentrations of the substrate, the electrode becomes a tool for the quantitative analysis of unknown concentrations of that same substrate.
Enzymatic peroxidation requires two substrates: oxygen, which is usually present in excess, and the unknown, for which the enzyme is specific and which is usually present in a limited amount. In operation, the enzyme is placed in an oxidized state before reacting with a substrate. Then, after enzyme-substrate interaction, the enzyme is reduced. This reduced enzyme is re-oxidized in order to produce hydrogen peroxide. If oxygen were not present, the catalytic enzyme cycle would be inhibited.
In view of the above, it is desirable to provide an enzyme electrode apparatus for the analysis of glucose in an animal or human using the enzyme glucose oxidase. Such a device would be very useful in a program of diabetes management, relieving the diabetic of the need to obtain blood samples for glucose analysis.
In order to determine blood glucose concentration for diagnostic and other purposes, the present state of the art requires that blood samples be obtained. In a patient, samples are usually obtained either by pricking the finger or by intravenous withdrawal. However, these invasive methods are not satisfactory since tissue damage and patient discomfort often result.
A glucose oxidase-containing enzyme electrode apparatus has been previously constructed which is suitable for intravenous implanation. Such an apparatus, however, is not fully satisfactory since fibrous tissue growth and immune system rejection may inhibit proper functioning of the apparatus over long periods of time.
As a non-invasive alternative, the measurement of blood glucose concentration at a body surface may be used. This is achieved without the necessity of obtaining a blood sample. Body surface areas that may be suitable include the skin and the mucous membranes.
It is generally known that glucose diffuses from subdermal capillaries onto the surface of hydrated skin. This was shown by experiments which consisted of placing drops of buffer solution (which contained enzymes and coenzymes used in the enzymatic analysis of glucose) onto the skin, and then measuring the increase in fluorescence as NADP was reduced to NADPH. Significantly, although dry skin is an effective barrier to the diffusion of hydrophilic molecules such as glucose, that barrier is reduced by the removal of keratinizized layers, thereby leaving only the dermis. However, the buccal mucosa and the dermis have nearly identical diffusion characteristics for many hydrophilic molecular species, including glucose.
Accordingly, it is an object of the present invention to provide a method for measuring blood glucose concentration using glucose which is present at the buccal mucosal surface of a living being.
It is another object of the present invention to provide a method for measuring blood glucose concentration by means of the peroxidative enzyme glucose oxidase.
Still a further object of the present invention is to provide a method for measuring blood glucose concentration which is non-invasive.
Yet another object of the present invention is to provide a method of measuring blood glucose concentration using an excess oxygen supply.
It is still a further object of the present invention to provide a method of measuring blood glucose concentration by means of an electrode apparatus.
Still other objects of the invention will in part, be obvious, and will, in part, be apparent from the following description.